Just offering an API does not guarantee developers will use it. Paul Miller from Talis points out that "Nothing says someone will develop with an API just because you open it. You need the infrastructure, community and technical support around it. [For developers] the API has to do something you want, easier or better than you could it yourself, or bring some other benefits on the side." If you look at the popularity of APIs in our sample you'll see that there's a big difference in adoption across APIs.

An API can be both a product and a distribution channel. As such it needs to have something to offer the developer. Chris Saad from DataPortability.org said that "if the network has no users, then it will have no developers...the reason dev platforms attract developers is because of their promise of distribution." For some classes of service-based APIs like Amazon's S3 or Google Maps this is not an issue, they provide value unto themselves. Mashup developer Taylor McKnight points-out that code reuse and time-to-release are valuable benefits of an API: Why reinvent the wheel when there are wheels available for the taking?" And because this is the end a business relationship, Oren Michels of Mashery and the Business of APIs Conference notes "One opens an API as a business development initiative, and so evaluating its success should be based on how it performs in that context."

It takes investment and commitment. Not just creating the API in the first place but supporting it, supporting developers using it, upgrading it, and doing this over the long haul. The major API providers know this and that's why there are big events now like platform-specific developer days.

Is it for serious development? The popularity of map mashups and lightweight Facebook apps drive this question. But Esther Schindler, of CXO Media, made the apt point that "ANY development can be lightweight crap. Using APIs isn't really part of that issue. It's all a question of good design."

The importance of open standards. The best APIs leverage open standards extensively. From the basics like RESTful HTTP and XML to newer ones like JSON and OAuth.

It's a good overview which in its breadth points out how much discussion and debate there is in this fast moving market as well as how it's only just getting started.